The possibility of identifying user geographical location in wireless communication networks has enabled a large variety of commercial and non-commercial services, e.g., navigation assistance, social networking, location-aware advertising, emergency calls, and the like. Different services may have different positioning accuracy requirements imposed by the application. In addition, regulatory requirements exist in some countries on the positioning accuracy for basic emergency services, i.e., FCC E911 in US. Positioning methods include GPS or Assisted-GPS (A-GPS), for User Equipment (UE) or other devices which include a GPS receiver circuit. Since not all UE are equipped to receive and process GPS ranging signals, other positioning methods have been standardized by 3GPP, such as Observed Time Difference of Arrival (OTDOA), in which a UE measures the relative timing of reference signals transmitted from different base stations. The UE (or a location services network node) can then estimate the UE position based on the measured signal arrival timings.
An advance in wireless communication technology, which promises improved bandwidth and higher signal quality, is multi-carrier transmission, in which two or more signals are modulated onto different carrier frequencies and transmitted simultaneously. Generally, one carrier frequency (or simply “carrier”) is designated as a primary carrier (also known as the anchor carrier), and other carriers are considered secondary carriers (also known as component carriers). For load balancing and other network management reasons, a network may switch the carriers for individual UEs—e.g., assigning a particular carrier as the primary carrier for one or more UEs, and a secondary carrier for other UEs. This carrier switching is dynamic, and may include switching primary carrier between different Radio Access Technologies (RAT), e.g., between LTE and HSPA.
In prior art multi-carrier wireless communication networks, the impact on the positioning measurements is not considered in primary carrier switching decisions. As a consequence, ongoing positioning measurements may be interrupted or delayed when carriers are switched. Furthermore, reference signals used in some positioning methods, such as OTDOA, are not transmitted on all carriers. Accordingly, a UE's primary carrier could be switched from a carrier transmitting Positioning Reference Signals (PRS) to a carrier that does not transmit PRS, forcing the UE (or other device) to obtain positioning measurements in measurement gaps on a secondary carrier. Positioning measurements obtained on a secondary carrier may have less strignent requirements, may be inconsistent, and may take longer to acquire and process than those obtained from a primary carrier transmitting PRS. This can adversely affect both the rapidity and quality/accuracy of UE positioning procedures.